Senate Banking Chairman Is Expected to Retire

WASHINGTON—Sen. Tim Johnson (D., S.D.), chairman of the powerful Senate Banking Committee, is expected to announce Tuesday he won't seek re-election in 2014, according to two Senate Democratic aides, setting the stage for a hotly contested race to succeed him.

Mr. Johnson, 66 years old, is slated to speak Tuesday afternoon at the University of South Dakota, his alma mater, to discuss his plans. A spokesman declined to comment on what...